1. Field of the Invention
The present invention relates to apparatus and methods for intermixing flows of fuel and air; and, more particularly, it relates to such apparatus adapted for use with internal combustion engine carburetors.
2. Discussion of the Prior Art
Internal combustion engines, for example, those used in automobiles, normally employ some type of carburetor which meters and intermixes flows of fuel and air to the engine. As the mainstream supply air, which is usually regulated by a butterfly valve, flows through a venturi portion of the carburetor, fuel is drawn into the carburetor through one or more fuel jets from a float controlled reservoir. The venturi portion, through which the air and entrained fuel flow at high velocities, is largely responsible for atomization of the fuel into air flow; that is, for breaking up the streams of liquid fuel into very small droplets and for dispersing these droplets throughout the air flow.
For effectively atomizing the fuel and dispersing the fuel droplets in the air flow, it is generally agreed that the flow velocity through the carburetor venturi be nearly sonic, and also that such sonic flow occurs when the vacuum in the engine intake manifold, into which the carburetor discharges, is equal to about 14.3 inches of mercury. This is discussed, for example, in the patent by Eversole et al (U.S. Pat. No. 3,778,038), in which is discussed various well-known problems associated with incomplete atomization of the fuel and inadequate mixing of the fuel droplets into the air flow, both of which are common occurrences unless the chamber venturi vacuum exceeds about 12 inches of mercury.
As an illustration of effects of such known problems, even though a carburetor may provide a fuel to air ratio theoretically calculated to provide substantially complete combustion of the fuel in the engine, a poorly atomized fuel flow and an inadequate mixing of the fuel into the air flow, usually causes a fuel-air mixture flow to some engine cylinders which is too fuel rich to burn--often even including liquid fuel itself--and a flow to other cylinders which is too fuel lean to burn. These conditions are worsened and made more prevalent when, upon acceleration, extra fuel is pumped by an acceleration pump into the carburetor, and also by asymmetrical positioning of the butterfly valve which acts as an obstruction.
Wheter incomplete fuel combustion is caused by a too rich or a too lean mixture, the effect is the same: discharging of unburned hydrocarbons into the atmosphere through the engine exhaust. This wastes increasingly expensive fuel and is wasteful of an important natural resource which is becoming increasingly scarcer.
In addition, and to many even more importantly, the discharged unburned fuel becomes a major source of air pollution, it being commonly acknowledged that substantial amounts of the gasoline used by automobiles are currently discharged as hydrocarbons into the atomosphere because of incomplete combustion in the engine. Although even with complete fuel combustion, pollutants such as carbon monoxide and dioxide are emitted into the air, these are considered generally harmless when compared to other fuel pollutants.
One often suggested way to eliminate at least some of the air pollution due to incomplete fuel combustion has been to mix additional air into the fuel-rich exhaust gases and ignite the mixture in an exhaust "after-burner". There are, however, many practical problems associated with implementing this technique. In addition, afterburning does not directly attack the problem of poor combustion in the engine---that is, the basic problem of poor fuel-air intermixing--and neither utilizes the exhausted fuel to advantage nor prevents its wastage.
Another technique that has been widely used, in an attempt to provide more effective mixing of the fuel into the air by enhancing the vaporization of the fuel, has been to heat the carburetor or portions thereof and/or the intake manifold by engine generated heat recovered from either the engine exhaust or cooling systems. However, even with such heating, thorough fuel and air intermixing is at best rarely achieved, largely because the heated surface area--walls of the carburetor or intake manifold--is not large compared to the volume of the carburetor and manifold intake, and insubstantial heating of the fuel usually occurs. At best, such heating techniques are stopgap attempts to overcome conventional, inefficient carburetor designs.
These inefficiencies largely relate to the fact that commonly used carburetors have fixed cross section venturi portions in which most of the fuel-air mixing occurs. The fixed cross sectional area of the venturi is selected by compromising among various different anticipated engine operating conditions, and attempting to provide substantially sonic venturi flow under the most prevalent, expected operating conditions. As a consequence, the venturi cross sectional area is often too great to provide sonic flow and good fuel-air mixing for many conditions, particularly those conditions, such as acceleration, when large quantities of fuel are introduced into the carburetor without corresponding large quantities of air.
Recognizing the basic problem associated with fixed cross sectional area venturi, various disclosures provide a variable cross sectional area venturi for carburetors; venturi whose cross section may be automatically changed in response to engine demand for fuel and air. By such expensive control means, sonic flow through the venturi should be maintainable over wide engine operating ranges. Examples of such disclosures include that of Eversole et al, mentioned above, and those of Barnes, Jr., Shaw, Mock, Stresen-Reuter, Kimberley, Rhodes et al, Pelizzoni, Kincade, Hartshorn, Harrison and Freismuth, et al (U.S. Pat. Nos. 3,911,063; 2,066,544; 2,118,220; 2,468,416; 2,525,083; 3,464,803; 3,880,962; 3,659,572; 3,778,041; 2,052,225; 3,896,105; and 3,841,612, respectively). Such activity in this field is evidence of the considerable magnitude of the problem and the potential benefits which should be achievable.
Still other disclosures relate to use of generated sound waves, usually ultrasonic, to agitate the fuel-air flows and enhance the breaking up of the fuel into very small droplets and the dispersing of the droplets into the air by application of sound wave energy. Examples of such disclosures include those of Cottell, Thatcher, Fruengel, Grieb and Bartholomew (U.S. Pat. Nos: 2,756,575; 3,907,940 and 3,533,606; 3,908,433; 2,791,944; and 3,834,364, respectively). Again, the activity in this particular area attests to the magnitude of problems with conventional carburetors and the potential benefits to be gained.
The amount of activity in these mentioned fields of endeavor also is indicative, however, that the problems associated with poor carburetor fuel-air mixing have not yet been satisfactorily solved. For instance, many types of variable cross section venturi, while potentially providing sonic flow over wide operating ranges, lack homogenizing means and thus give rise to inadequate intermixing. Also, at least some of the fuel-air intermixing and much of the fuel vaporization is associated with fuel flow along surfaces of the venturi, and even variable cross section venturi having appropriate characteristics to assure velocity under most engine operating conditions still have such relatively low surface to volumetric flow rates that mixing of fuel vapor is not optimized, particularly for fuel rich flows. And, while addition of sonic wave energy may assist fuel atomization and dispersion, sonic wave energy alone appears unable to provide substantially homogeneous intermixing and fuel vaporization under most engine operating conditions.
For these and other reasons, to achieve optimum fuel economy and to substantially reduce air pollution by substantially homogeneous fuel-air intermixing and fuel vaporization into the air flow at substantially all engine operating conditions, improvements to engine carburetor systems, beyond those currently used and previously disclosed, are still necessary.